Upon finding the body, officers identify themselves as 3 William 56. SVU detectives then find an invitation for someone named Riggs, which is the name of Mel Gibson's character in Lethal Weapon. The car in which Riggs rides in is 3 William 56.
To add to the previous poster, the victim is Vicky Riggs, the name of Martin's deceased wife, and who we never see on-screen in the Lethal Weapon movies.
The pool into which Rebecca De Mornay's character is dumped is at the Pleasantdale Chateau in West Orange, NJ - and is the same pool in which 'Wilfred Brimley' and the others frolicked in the movie "Cocoon (1985)"
Mariska was pregnant with her first child during the filming of this episode. You can see that they tried to cover her in many different ways. Carrying files, buttoned up coats, and in one scene, she leans over a body and then pulls her jacket together to cover her belly.
3 William 56 is the call for Mel Gibson and Danny Glover in Lethal Weapon. The victim is Vicky Riggs, Mel Gibson's deceased wife in Lethal Weapon was Victoria Riggs.